CustomPainter.dart

Container(
  height: kToolbarHeight,
  child: Row(
    children: <Widget>[
      Flexible(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: CustomPaint(
            size: Size.fromHeight(kToolbarHeight),
            painter: CirclePainter(100 - percent),
          ),
        ),
      ),
    ],
  ),
),